Suppose we replace the mass in the video with one that is four times heavier. How far from the free end must we place the pivot to keep the meter stick in balance?

90 cm (10 cm from the weight)

Explanation:

For the meter stick to be in balance, a zero figure on the net torque must be achieved. Torques about the fulcrum may be applied by the mass hanging from the ending of the stick and also by the stick's initial weight. We utilize the condition that the net torque has to be equal to zero to attain a relationship involving

1) The space amid the left end of the stick and that of the fulcrum

2) the space between the center mass of the stick and that of the fulcrum.

These two distances is expected to add up to a constant.